This application claims benefit of Japanese Application No. 2001-154371 filed on May 23, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a lens barrel for a camera or the like equipped with a plurality of lens frames capable of moving in the direction of an optical axis, wherein the lens barrel is configured such that the lens frames are securely linked to each other.
2. Description of Related Art
In conventional practice, lens frames are often connected to each other by helicoid threads to allow the lens frames to move smoothly in the direction of the optical axis in the lens barrel of a zoom lens and the like of a camera.
A technique in which not only backlash play (that is, play in the thrust direction), but also radial-fit play (that is, play in the radial direction) can be eliminated by causing a roller fitted onto a roller axle to engage one of the faces of the helicoid thread provided to one of the frames is disclosed, for example, in Japanese Patent Laid-open Publication No. 58-118612 as a conventional connection means involving the use of such helicoid threads.
It should be noted, however, that large forces are applied to the joints between the lens frames in such lens barrels when the user accidentally drops the camera or the camera is subjected to an impact or shock.
Screwed joints formed by helicoid threads must therefore be prevented from being easily disengaged in order to allow lens frames to remain connected when an outside force acts in a direction in which the threaded engagement between the helicoid threads may be loosened.
The above-described example of the prior art is disadvantageous in that it is aimed solely at eliminating play in the thrust direction and play in the radial direction and in that it lacks the function of preventing the joint between the lens frames from being loosened. In addition, because the roller is configured to conform to the shape of the contacting helicoid threads, the roller tends to disengage in the same manner as the other portions of the helicoid threads.
An object of the present invention, which was perfected in view of the above situation, is to provide a lens barrel based on the use of a connection provided by helicoid threads, wherein the lens barrel is configured such that the connection provided by the helicoid threads can remain secured when a sudden outside force is applied to the lens barrel.
There is provided a first frame equipped with helicoid threads comprising a first helicoid thread having a ridge in which both flanks of the ridge are formed at a first flank angle, and a second helicoid thread having a ridge in which both flanks of the ridge are formed at a second flank angle which is different from the first flank angle; and a second frame provided with helicoid threads in screwed-state engagement with the corresponding first and second helicoid threads on the first frame.
The above and other objects, features, and advantages of the invention will become more clearly understood from the following description referring to the accompanying drawings.